DE 10 2004 023 621 A1 discloses a method and device for determining the energy content of an energy storage device. Said document describes a concept for determining the charge state of a battery in a vehicle but does not mention a strategy for correcting a low charge state or for improving the efficiency level of the electrical system or drive. The charge state is continually estimated and output as a precise numeric value. The estimation of the charge state can be corrected by means of galvanically decoupling the battery from the electrical power source. The correction can be applied periodically or it can be scheduled in a sporadic manner if a favorable driving section lies ahead. The correction is implemented by means of measuring the no-load voltage of the battery. The charge state is a function of the no-load voltage if there has not been any load on the battery for a sufficiently long period of time. The charge state is determined by means of integration of the battery current between the correction processes. The charge state is used as the initial value of the integration process after said charge state has been corrected (measuring the no-load voltage and determining a charge state).
U.S. Pat. No. 6,646,419 B1 discloses a method for determining the charge state of a lead acid battery in a vehicle. This method also continuously estimates the charge state and outputs the result as a precise numeric value. Also, the charge state is determined by means of integrating the charging current or the discharging current respectively. The secondary battery current that is involved in the gas formation and the heating up of the battery is calculated but not stored. The difference between the total battery current and the secondary battery current produces the charging current or discharging current that is integrated in the case of determining the charge state. Also, the initial value of the charge state is determined from the no-load voltage of the battery following a phase where the battery current is zero or low. If the vehicle has been switched off for a long period of time, a new value is calculated for the initial value of the charge state from the no-load voltage. This document also describes that the initial value of the charge state can be corrected during the driving operation. The no-load voltage of the battery is estimated using the measured battery current after a long phase where the battery current is zero. The document does not describe in detail if the estimated terminal voltage is used in order to correct the initial charge state.
U.S. Pat. No. 8,159,188 B2 discloses a method for controlling the charge state of a lithium ion vehicle battery so that it is also always possible to achieve a minimum discharging current value. The method ensures in aging batteries that said batteries can always deliver sufficient discharging current. The charge state of the battery is maintained at a value between a minimum and a maximum charge state. If it is determined that a required discharging current cannot be achieved, the minimum charge state is increased in a part load operation. The increase is a function of the difference between the required current and the supplied current, the battery temperature, the charge state and other battery conditions.
U.S. Pat. No. 8,638,070 B2 discloses a method for adaptively charging a battery to a desired value. The charge state is estimated and output as a precise numeric value. The estimation is performed by means of actively controlling the terminal voltage of the battery by means of a sequence of charging and discharging pulses. The pulses have a predefined current profile and the voltage response of the pulses are used in order to estimate the charge state. The charging or discharging pulses respectively must generate voltage responses within narrow tolerances. Their exact form is continuously adapted so that the responses remain within the tolerances. The pulses are always implemented periodically or rather independently from the operating state of the entire system. Due to the fact that the voltage response to a predetermined current is used in order to estimate the charge state, a relationship between the equivalent capacitances of the battery and the charge state are used in order to perform the estimation. This method was developed for lithium ion batteries and it is intended that it can also be used for other battery types such as Ni-MH. However, there is no mention of lead acid batteries.